1. Field of the Invention
The present invention relates to a link implement between a base station and a base station controller in a digital mobile communication system such as digital cellular system (DCS) or personal communication system (PCS) and, more particularly, to a fractional E1 link device between a base station and a base station controller, in which the E1/T1 links between the base station and the base station controller are divided by time slots.
2. Description of the Related Art
In a digital mobile communication system (e.g., DCS or PCS), the full E1/T1 link between a base station and a base station controller is used to transmit and receive data in a framed and unchannelized manner, with the transmission/reception data being in the form of HDLC.
The digital mobile communication system has a network structure that the full E1/T1 link is assigned to all base stations irrespective of the capacity of the individual base stations.
The full E1 link consists of 32 time slots each of which has a capacity of 64 Kbps in (FIG. 4). The full T1 link consists of 24 time slots each having a capacity of 64 Kbps in (FIG. 3).
However, every subscriber in the code division multiple access (CDMA) digital mobile communication system has a capacity of about 21.368 Kbps.
In the CDMA system, data are transmitted and received in the form of packet over E1/T1 trucks between the base station and the base station controller. The individual packets have a structure as presented in Table 1.
The packet gap is 6 bytes in the packet-based data communication system.
Also, traffic data appears every 20 ms in the CDMA system and the traffic varies depending on the activity of the voice as presented in Table 2.
The traffic in the CDMA system includes traffic data of the subscribers and control data for control of the traffic data. The individual packets have a pattern of IPC packet, which is a modified HDLC. Thus the characteristic of the HDLC must be taken into consideration in calculating the actual data rate over the truck.
The actual data rate is determined as follows:
In the calculation, traffic data, HDLC-related zero insertion and flag, CRC (FCS) and packet gap are necessary.
Traffic={(52xc3x970.291)+(40xc3x970.039)+(35xc3x970.072)+(32xc3x970.598)}xc3x978 bits Zero insertion (3% assumption)=traffic per one channel (excepting flags)xc3x970.03=9 bits Packet gap=6 bytes=48 bits Assuming that the control packet appears with 50% of the occurrence probability of the traffic packet, HDLC-related zero insertion and flag, CRC and packet gap.
Traffic per one channel=148xc3x978 bits=1184 bits Zero insertion (3% assumption)=traffic per one channel (excepting flags)xc3x970.03=35 bits Packet gap=6 bytes=48 bits The average packet length amounts to 1268 bits and appears 2.5 times per second with 50% of the occurrence probability of the traffic packet, at the data rate of 3168 bps.
As well known in the art, one channel has a capacity of 21.368 Kbps.
The generated packet data are transmitted to the trunk on the E1/T1 link in an unchannelized manner.
In transmission over the E1 link, the gross data capacity is 1920 kbit (=2048 kbitxe2x88x92128 kbit) (excepting time slots 0 and 16) with a traffic channel capacity of 90 channels (=1920 kbit/21.368 kbit).
In transmission over the T1 link, the gross data capacity is 1536 kbit (=1544 kbitxe2x88x928 kbit) (excepting flame bits) with a traffic channel capacity of 72 channels (=1536 kbit/21.368 kbit).
That is, the maximum number of subscribers is 90 on the full E1 link and 72 on the full T1 link.
Accordingly, this trunk line has an excess of capacity relative to a base station of a low capacity designed to support no more than 20 to 40 subscribers. Such a waste of capacity of the trunk line causes a rent cost for unnecessary designated links, resulting in a considerable economic loss of the mobile communication company.
It is, therefore, an object of the present invention to provide a fractional E1 link device between a base station and a base station controller, in which the E1/T1 links between the base station and the base station controller are divided by time slots.
To achieve the above object of the present invention, there is provided a fractional E1 link device between a base station and a base station controller in a ink interface between the base station and the base station controller for a mobile communication system the fractional E1 link device including: a clock converter for receiving a frame sync clock and a system clock, and converting the system clock to a clock corresponding to the number of subscribers; a processor in synchronism with the output clock of the clock converter, for interfacing transmission/reception data of the base station; a framer/transceiver in synchronism with the frame sync clock and the system clock, for framing the output data of the processor to specific time slots in conformity with a fractional E1 link, and transmitting data received on the fractional E1 link to the processor; and a multiplexer/demultiplexer for multiplexing data received from a different base station from that of the framer/transceiver, transmitting the multiplexed data on a E1/T1 link, demultiplexing data received on the E1/T1 link, and transmitting the demultiplexed data to the framer/transceiver of each base station.
In another aspect of the present invention, there is provided a fractional E1 link device between a base station and a base station controller in a link interface between the base station and the base station controller for a mobile communication system, the fractional E1 link device including: a clock converter for receiving a frame sync clock and a system clock, and converting the system clock to a clock corresponding to the number of subscribers; a processor in synchronism with the output clock of the clock converter, for interfacing transmission/reception data of the base station controller; a framer/transceiver in synchronism with the frame sync clock and the system clock, for framing the output data of the processor to specific time slots in conformity with a fractional E1 link, and transmitting data received on the fractional E1 link to the processor; and a multiplexer/demultiplexer for multiplexing data received from a different base station controller from that of the framer/transceiver, transmitting the multiplexed data on a E1/T1 link, demultiplexing data received on the E1/T1 link, and transmitting the demultiplexed data to the framer/transceiver of each base station controller.